Treating thiocyanates



Patented Jan. 10, 1933 UNITED STATES PATENT OFFICE CHRISTIAN J. HANSEN,OF ESSEN-ON-THE-RUHR, GERMANY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THEKOPPEBS COMPANY OF DELAWARE, OF PITTSBURGH, PENN- SYLVANIA, ACORPORATION OF DELAWARE TREATING THIOOYANATES No Drawing. Originalapplication filed August 9, 1928, Serial No. 298,617, and. in GermanyApril 14, 1928. Divided and this application filed November 29, 1929.Serial No. 410,651.

My invention refers to the treatment of thiocyanogen compounds and moreespecially ammonium thiocyanate, whereby a decomposition of suchcompounds is obtained and sulphur and the corresponding sulfates, suchas ammonium sulfate, are recovered. It is an object of my invention toprovided means whereby this decomposition of the thiocyanogen compoundsand conversion into sulfates and free sulfur can be effected in asimpler and more efficient manner and at lower cost, than was hithertopossible.

Hitherto solutions of ammonium thiocyanate, such as resulted forinstance in the purification of gases developed in the distillation ofcarbon and other carbonaceous material, have been subjected tohydrolytic decomposition by heating same with acids, more especiallywith dilute sulfuric acid. This decomposition results in the formationof ammonum sulfate and carbon oxysulfide, whch is partly decomposed inthe presence of water into carbon dioxide and hydrogen sulfide. This wayof proceeding entails the drawback that it requires a considerableoutlay for the sulfuric acid required in the decomposition, and thesulfur compounds resulting in the reaction must be subjected separatelyto further treatment.

This is a division of the application Serial No. 298,617, filed August9, 1928, in which I have described a. generally applicable method ofdecomposing thiocyanates and of forming ammonium compounds therefrom byheating an aqueous solution of such thiocyana-tes in the presence ofcompounds containing the radical S0 According to the present inventionthe reactive nitrogen and the sulfur contained in thiocyana-tes can berecovered in the form of ammonium sulfate and free sulfur in aparticularly simple and effective manner requiring no separate reagentssuch as sulfuric acid. Moreover, this conversion can be obtained in asingle operation.

I have ascertained that if ammonium thiocyanate or other thiocyanatesare heated with water in the presence of a bisulfite and at least onethionate such as thiosulfate and/or polythionate, the occurringhydrolytic reaction, viz.

is promoted to such an extent, that the thiocyanate is almost completelyconverted into ammonium sulfate and sulfur at a rapid rate. The sameeffect is obtained, if part of the bisulfite is replaced by a sulfite.

Mixtures of bisullite, sulfite and thionates are known to be decomposed,on being heated, into sulfates and free sulfur, with or without aconcomitant formation of free sulfuric acid. In the practice of myinvention, however, all these reactions occur simultaneously and promoteeach other considerably. This valuable result is apparently due to theinstantaneous and continuous absorption, by the bisulfite and thionatemixture, not only of the ammonia, but also of the hydrogen sulfidedeveloped in the hydrolytic reaction, mentioned above.

1 It is well known that a complete decomposition of the mentionedderivatives of sulfur dioxide into sulfate and free sulfur requirespredetermined proportions of the several constituents, i. e. that foreach molecule of a polythionate two molecules of sulfite or thiosulfateand for each two molecules of a bisulfite one molecule of sulfite orthiosulfate be present. If the quantities of sulfite or thiosulfate insolution are greater, complete decomposition is not possible inasmuch asin that case the solution contains besides sulfate also non-decomposedthiosulfate. If there is polythionate or bisulfite in excess in thesolution, there is formed, when operating in closed vessels, besidesammonium sulfate a corresponding quantity of free sulfuric acid.

Before going into the details of my invention and how the same iscarried out in practice, I will first explain the facts on which thisinvention is based.

First of all I found that ammonium thiocyanate can be decomposed in aquantitative manner by heating an aqueous solution thereof with sulfurdioxide, ammonium bisulfite or ammonium thiosulfate in combination withsulfur dioxide.

The following equation serves to illustrate this decomposition:

This reaction can be explained as follows:

The decomposition of thiocyanic acid occurs according to the equation:

II. HCNS +H O NH COS Carbon oxysulfide is further decomposed in contactwith water according to the equation:

III. COS+H O==CO +H S Thus from lHCN S is finally formed INH and IH S Ifammonium thiocyanate is treated in this way, 2NH, and H1 3 will result.

In order to produce 1(NH SO from NH CNS, the sulfur dioxide must firstbe converted into SO according to the equation IV. 380 230 S Thereforein order to obtain 1SO 1,5 S0 is required, which results in 1SO 0.58.

Further in order to convert the hydrogen sulfide obtained in thedecomposition of COS (Equation III) into sulfur, I require according tothe equation:

additional 0, 5 CO per molecule ammonium thiocyanate.

If the above quantities of S0 are added, there resuits, that permolecule ammonium thiocyanate 2SO are required, which fur nish0.5+l.5=2S.

- The above proves that Equation I is covered.

In order to carry this process through, 230 must be produced byoxidation of 28 per molecule ammonium thiocyanate. However, as just 28are recovered in the process in the form of elementary sulfur, noextraneous sulfur at all is required in the process The conversionaccording to Equation I takes place slowly at ordinary temperature,while at 100 C. about per cent of a 20 per cent solution of NH CNS willbe decomposed in eight to ten hours. At a temperature between 180 and200 C. the ammonium thiocyanate will be decomposed quantitatively in notmore than two hours.

If operating with polythionate instead of sulfur dioxide, the reactionoccurs according to the following equation:

This reaction can be explained as follows:

According to the equation VII. (NH S O (NIL) SO +SO +S 1 moleculetrithionate when heated, is decomposed into 1 molecule sulfate, 1SO +1S.If higher polythionates are used, the same compounds will result, but inthat case more sulfur is obtained, for instance in the case oftestrathionate 25, in the case of pentathionate 3 The Equation VII thusshows that here 1 polythionate is equivalent of 1SO The Equation VIfurther shows that by using trithionate 48, by the use of tetraandpentathionate 6 and 8S respectively are obtained.

The production of a polythionate, such as the trithionate fromthiosulfate occurs according to the following equation:

This reaction occurs in several intermediate steps, only one of whichhas hitherto been ascertained. When introducing sulfur dioxide into asolution of thiosulfate, in contradistinction to the treatment ofthiosulfates with other acids no or very little sulfur will at firstseparate, and the solution will remain limpid and will at the same timeassume a deep yellow color. The solution now contains an additivecompound of 1 molecule thiosulfate and 1 molecule 80;. The pol thionatewill form from these two compoun s, the formation occurring slowly atordinary temperature and more rapidly upon heating.

If it is desired to produce sulfate from thiosulfate by way of apolythionate, the simplest method is that which follows the equation:

' 3(NH4) 2SO,+4S

In order to satisfy this equation merely onethird of the t-hiosulfatemust be converted into polythionate with the aid of sulfur dioxide.According to Equation VIII each molecule polythionate to be producedrequires 1,580 which shows that in order to convert thiosulfate intosulfate, 0.5 S0 must be added per molecule thiosulfate.

Takin into consideration the Equations VIII an IX, the conversion ofthiosulfate into sulfate occurs according to the equation:

The uations VI and VIII further show that a mixture of ammoniumthiosulfate and ammonium thiocyanate can be converted by means of sulfurdioxide into sulfate and sui fur according to the equation:

This equation shows how ammonium thiosulfate and ammonium thiocyanatecan be converted, directly into sulfate and su'ifur by acting withsulfur dioxide.

ite

iiso

I may however also convert ammonium thiocyanate into sulfate and sulfurwith the aid of ammonium bisulfite according to the equation:

XII. N H ONS 8NH HSO3 5 2804+ 002 i is.

This reaction can be explained as follows:

As shown in Equation I, 2SO are required per molecule NH ONS. On theother hand a mixture of 1 molecule ammonium sulfite and 2 moleculesammonium bisulfite when heated, will also be converted into sulfate andsulfur according to the equation:

Now as lNI-LONS requires 2SO the double of the quantities shown inEquation XIII must be used. The 2SO are bound by the sulfite which isthus converted into bisulfite. This shows the way, in which the 8NH HSO3are required according to Equation XII per molecule NH ONS.

All these conversions of ammonium thionate take place slowly at ordinarytemperature, more rapidly at an elevated temperature. At about 100 C.about one-half of the ammonium thiocyanate is decomposed withi eight toten hours, while at ISO-200 O. the conversion will be completed in oneto two hours, all ammonium thiocyanate having disappeared.

If less sulfur dioxide, bisulfite or polythionate is used thancorresponds to the respective equations, the reaction will be completeand the liquor will usually still contain ammonium thiosulfate andnon-decomposed ammonium thiocyanate. On the other hand an excess ofsulfur dioxide, isulfite of polythionate will not be harmful, theconversion being quantitative and the excess of sulfur dioxide beingconverted into sulfuric acid and sulfur according to Equation IV. Inthis case the liquor contains more or less sulfuric acid, which can beneutralized by adding ammonia before evaporation.

The process is preferably carried through at a temperature whichmaterially exceeds 100 C., for instance at 140160 or above, and underincreased pressure. The ammonium thiocyanate may be contained in theliquor from the beginning. If in the purification of coal distillationgases the contents of cyanogen compounds are recovered separately underthe form of ammonium thiocyanate, the solution thus obtained may beadded to the washing liquor serving for removing from the gas ammoniaand hydrogen sulfide, provided that it contains or is incorporated withbisulfite and, if desired, with sulfite. One may however also conductthe washing process in such manner that the contents of cyanogencompounds, ammonia and hydrogen sulfide in the gases are washed out in asingle operation, whereupon bisulfite and sulfite are added.

On the other hand, if the ammonium thiocyanate is recovered in aseparate washing operation, it is also possible to force the solution ofammonium thiocyanate thus obtained into the heated decomposition vesselcontaining a solution of bisulfite and a polythionate. In a similarmanner a polythionate solution containing ammonium thiocyanate, whichmay be preheated if desired, may also be forced into the heatedconversion chamber, containing a solution of bisulfite.

Example 1 A solution of 100 kgs. ammonium thiocyanate, 2083 kgs.ammonium bisulfite, 610 kgs. ammonium sulfite, 600 kgs. ammoniumtrithionate and 779 kgs. ammonium thiosulfate in 5000 kgs. water whichis contained in a closed pressureresisting vessel, is heated to about180 C. After four to six hours all the thiocyanateisdecomposedintosulfate and free sulfur. The resulting watery liquidcontains 3300 kgs. ammonium sulfate and there are further obtained 674kgs. pure molten sulfur and 57.8 kgs. carbon dioxide, which may betapped ofi.

I may also introduce one or more of the sulfur dioxide derivativesgradually during the heating period.

If the reaction is carried through at 220 O, the conversion will alreadybe complete within one or two hours, while at a lower temperature alonger heating is required.

Example 2 A solution containing 100 kgs. ammonium thiocyanate, 2083 kgs.ammonium bisulfite, 1557 kgs. ammonium thiosulfate and 600 kgs. ammoniumtrithionate in 5000 kgs. water is treated as described with reference toExample 1. There results a watery solution containing 3300 kgs. ammoniumsulfate and there are further obtained 807.5 kgs. pure molten sulfur and57.8 kgs. carbon dioxide.

Obviously the ammonium trithionate in the two examples could be replacedby tetrathionate or pentathionate the only change being that a greaterquantity of sulfur would be obtained.

Various changes may be made in the details disclosed in the foregoingspecification without departing from the invention or sacrificing theadvantages thereof.

In the claims aifixed to this specification no selection of anyparticular modification of the invention is intended to the exclusion ofother modifications thereof.

I claim 1. The method of decomposing thiocyanates and of producingammonium compounds therefrom comprising heating an aqueous solution ofsuch thiocyanates in the Y presence of a bisulfite, a polythionate and athiosulfate.

2. The method of decomposing thiocyamates and of producing ammoniumcompounds therefrom comprising heating an aqueous solution of suchthiocyanates under pressure to about 180220 G. in the presence gf abisulfite, a polythionate and a thiosulate.

3. The method of decomposing thiocyanates and of producing ammoniumcompounds therefrom comprising heating an aqueous solution of suchthiocyanates in the presence of a bisulfite, a sulfite, apolythionateand a thiosulfate.

4. The method of decomposing thiocyamites and of producing ammoniumcompounds therefrom comprising heating an aqueous solution of suchthiocyanates under pressure to about 180-220 C. in the presence of abisulfite, a sulfite, a polythionate and a thiosulfate.

5. The method of decomposing ammonium thiocyanates and of producingammonium compounds therefrom comprising heating an aqueous solution ofsuch thiocyanate under pressure to about 180220 C. in the presence ofammonium bisulfite, ammonium sulfite, sfm ammonium polythionate and athiosulate.

6. The method of decomposing ammonium thiocyanates and of producingammonium compounds therefrom comprising heating an aqueous solution ofsuch thiocyanate under pressure to about 180220 C. in the presence ofammonium bisulfite, ammonium sulfate, ammonium thiosulfate and anammonium polythionate.

In testimony whereof I afiix my signature.

CHRISTIAN J. HANSEN.

